// Filter cover for spotting scope.
// All dimensions in millimetres.

// Outer diameter of the scope objective end.
width = 31.9;

// How deep to make the ring.
height = 15;

thickness = 3;
gap = 1;

// Set arc smoothness limits for a better finish.
$fa = 3;
$fs = 1;

difference() {
  cylinder(d=width+gap+thickness, h=height);
  translate([0, 0, +1]) {
    cylinder(d=width+gap, h=height);
  }
  translate([0, 0, -height/2]) {
    cylinder(d=width-gap, h=height);
  }
}

